FDA Adjusts EUA for COVID-19 Antibody Treatment


The antibody combination COVID-19 treatment is the only one of its kind available in the United States.

The FDA has announced changes to its emergency use authorization (EUA) for the combination antibody therapy for mild-to-moderate COVID-19 (REGEN-COV; Regeneron Pharmaceuticals), lowering the dose to half of what the agency initially authorized.

The EUA changes now reflect a 1200 mg dose of the cocktail: casirivimab 600 mg and imdevimab 600 mg. The FDA’s decision was informed by data from several clinical trials, including a phase 3 trial demonstrating that the casirivimab-imdevimab combo therapy reduced the risk of hospitalization or death by 70% in high-risk non-hospitalized patients. Investigators also determined that the 1200 mg dose was consistent with the treatment effects of the original 2400 mg dose. Regeneron’s trials have treated over 9000 patients with casirivimab-imdevimab within and outside of the hospital setting. 

Casirivimab and imdevimab employ Regeneron’s VelocImmune and VelociSuite technologies to bind non-competitively to the key receptor binding domain of the SARS-CoV-2 spike protein, neutralize the virus, and protect against COVID-19 variants that have been circulating across the globe. Research currently in the pipeline is showing that the combination therapy is effective among the main variants circulating in the US, including the P.1 variant that was first cataloged in Brazil and the B.1.351 that was first identified in South Africa.

Who can receive the combination therapy? Individuals are eligible if they have certain medical conditions or fit certain demographic factors, such as based on race or ethnicity and therefore may be at high risk for severe disease progression. The National Institutes of Health (NIH) COVID-19 Treatment Guidelines Panel has also recommended the treatment for COVID-19 outpatients who have a high risk of clinical progression.

As for how patients with mild-to-moderate COVID-19 can receive the treatment, the updated EUA recommends intravenous (IV) infusion; however, subcutaneous (SC) injections can be used as an alternative should interruptions in IV infusion upset the treatment course.

Regeneron is expected to submit a Biologics License Application (BLA) in late summer 2021. In addition, although the EUA indicates that the treatment is only for non-hospitalized COVID-19 patients, studies are now evaluating whether casiriviamb-imdevimab has benefit in the prevention of COVID-19 and some hospitalized patient settings.

"Despite increased use of vaccines, thousands of patients are still becoming infected in the US every day, with many at high risk of serious complications from COVID-19,” said George D. Yancopoulos, MD, PhD, president and chief scientific officer at Regeneron. “Unfortunately, to date, only a fraction of patients eligible for antibody treatments have received them, which we hope will change based on this updated FDA authorization. REGEN-COV is readily available and supplied free of charge by the US government,” Yancopoulos said.

Health care providers are encouraged to familiarize themselves with the fact sheet for the combination therapy.


  1. FDA Authorizes Lower 1200mg Intravenous and Subcutaneous Dose of REGEN-COV (Casirivimab and imdevimab) Antibody Cocktail to Treat Patients With COVID-19. News Release. Regeneron; June 4, 2021. Accessed June 7, 2021. https://investor.regeneron.com/news-releases/news-release-details/fda-authorizes-lower-1200-mg-intravenous-and-subcutaneous-dose.

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